The present invention relates to a new process for the production of back foamed, deep drawn plastics useful as internal parts for refrigeration units.
Rigid polyurethane foam has been used for many years for the manufacture of refrigeration units and other refrigerating equipment because it has excellent heat insulating properties. In refrigerators, the rigid foam is also used as a structural material. The thermal conductivity of the rigid polyurethane foam, which has predominantly closed cells, depends to a large extent on the nature of the blowing agent or cell gas used. Blowing agents such as perhalogenated fluoro-chlorohydrocarbons (FCH), particularly trichlorofluoro-methane (R11) which has an exceptionally low thermal conductivity, have proven to be particularly suitable for the production of rigid polyurethane foams. These perhalogenated fluoro-chlorohydrocarbon materials are chemically inert and therefore non-toxic and incombustible. The stability of these perhalogenated fluoro-chlorohydrocarbons is, however, disadvantageous because they get into the stratosphere, where they contribute to the breakdown of the ozone due to their chlorine content (e.g. Molina, Rowland Mature 249 (1974) 810; First Interim Report of the Enquiry Commission of the German Federal Parliament "Vorsorge zum Schutz der Erdatmosphare" (Provisions for the Protection of the Earth's Atmosphere" of 02.11.1988, German Federal Parliament, Publicity Department, Bonn).